Polycarbonate (PC) is a high-performance plastic with good impact strength. In addition to ductility (impact strength), general-purpose PC has high transparency, good dimensional stability, low water absorption, good stain resistance and a wide range of colorability. A weak area for PC is its relatively limited range of chemical resistance, which necessitates careful appraisal of applications involving contact with certain organic solvents, some detergents, strong alkali, certain fats, oils and greases. Also, another weak area of PC is that it has a high melt viscosity which makes it difficult to mold. Medium to high flow PC grades suffer from the fact that the low temperature ductility is sacrificed for a better flow. Finally, PC formulations with visual-effect additives like metallic type pigments or mineral flakes are in general very brittle at room temperature. This invention deals with these shortcomings and as such proposes a material that has an unique property profile in terms of transparency, improved chemical resistance, higher flow and low, temperature ductility at −20 to −40° C., even with special-effect colorants.
A widely used method to increase low temperature impact resistance, is the addition of impact modifiers to the PC compositions. Adding minor amounts of methylacrylate-butadiene-styrene (MBS) rubbers or Acrylonitrile-butadiene (ABS) rubbers results in lower D/B transition temperatures. The major drawback of these modifications is that, even with only 1% addition levels, the transparency decreases, taking away one of the key properties of PC.
This opaqueness is caused by the relatively high refractive index (RI) of the aromatic PC (1.58) compared to the more aliphatic rubbery and/or siloxane components, which have R values in the range 1.48-1.56.
U.S. Pat. No. 6,040,382 describes how optical clarity of a blend of 2 transparent, immiscible, polymers can be improved by addition of a third polymer which is selectively miscible with one of the two original immiscible polymers. The concept is based on matching refractive indexes. This patent is directed to compositions of monovinyl aromatic-conjugated diene copolymers (like styrene-butadiene block co-polymers), styrene-maleic anhydride copolymers (SMA) and poly (alpha-methylstyrene).
U.S. Pat. Nos. 5,891,962; 5,494,969; and 5,614,589; respectively, describe specific formulations of rubber modified styrene; cycloolefin polymer composites; and methacrylate-acrylonitrile-butadiene-styrene copolymers with urethane copolymer. In these compositions, polymers are being replaced by co-polymers (f.i. polystyrene by a co-polymer of styrene and alkyl(methyl)acrylate) to match the RI of a rubbery component. It's also possible to modify the rubbery component to match the RI of the polymer matrix, like in U.S. Pat. Nos. 5,321,056 and 5,409,967 assigned to Rohm and Haas. The focus of all these patents is to chemically modify the ingredients to match RI to achieve transparency. Matching RI to achieve transparency is as such not a novelty.
U.S. Pat. No. 5,859,119 to Hoefflin relates to reinforced, molding compositions with desirable ductility and melt flow properties. The composition contains a cyclo aliphatic polyester resin, an impact modifying amorphous resin which increases the ductility of the polyester resin but reduces the melt flow properties thereof, and a high molecular weight polyetherester polymer which increases the melt flow properties of the polyester polymer without reducing the ductility thereof, and a glass filler to reinforce and stiffen the composition and form a reinforced molding composition. This invention is focussed on opaque PC blends, rather than transparent blends.
U.S. Pat. No. 4,188,314 describes shaped articles (such as sheet and helmets) of blends of 25-98 parts by weight (pbw) of an aromatic polycarbonate and 2-75 pbw of a poly cyclohexane dimethanol phthalate where the phthalate is from 5-95% isophthalate and 95-10% terephthalate. Articles with enhanced solvent resistance and comparable optical properties and impact to the base polycarbonate resin and superior optical properties to an article shaped from a polycarbonate and an aromatic polyester, such as polyalkylene terephthalate, are disclosed.
There are other patents that deal with polycarbonate polycyclohexane dimethanol phthalate blends for example; U.S. Pat. Nos. 4,125,572; 4,391,954; 4,786,692; 4,897,453 and 5,478,896. U.S. Pat. No. 5,478,896 relates to transparent polycarbonate blends with 10-99% polyester of CHDM with some minor amount of aliphatic diol and iso and terephthalic acid. U.S. Pat. No. 4,786,692 relates to a 2-98% aromatic polycarbonate blend with a polyester made of cyclohexane dimethanol (CHDM) and ethylene glycol (EG) in a 1:1 to 4:1 ratio with iso and terephthalic acid. U.S. Pat. No. 4,391,954 describes compatible compositions of non halogen polycarbonate (PC) and amorphous polyesters of CHDM and a specific iso/tere phthalate mixture. U.S. Pat. No. 4,125,572 relates to a blend of 40-95% PC, 5-60% polybutylene terephthalate (PBT) 1-60% and 1-60% an aliphatic/cycloaliphatic iso/terephthalate resin. U.S. Pat. No. 4,897,453 describes blends of 10-90% PC, 10-90% of a polyester of 0.8-1.5 IV, comprised of 1,4-cyclohexane dicarboxylic acid, 70% trans isomer, CHDM and 15-50 wt. % poly oxytetramethylene glycol with 0-1.5 mole % branching agent. Also claimed are molded or extruded articles of the composition.